This invention relates generally to gas discharge systems and, in particular, to cathodoluminescent systems wherein a gas discharge is used as an electron source from which electrons are extracted for acceleration toward a designated target.
In many cases where electrons are extracted from a gas discharge for use in bombarding a target, the electron beam so formed is modulated by a control voltage prior to being accelerated toward the final target. Such modulation may be effected by interposing an electron-transmissive control grid between the extracted electrons and the target. By varying the voltage on the control grid, the number of electrons which pass through it can be varied.
A problem with such prior art gas discharge systems is the large control voltage change which is required to effectively modulate the electron beam. In some applications, particularly those where the control voltage need not be varied rapidly, the requirement of a large control voltage is not a serious disadvantage. However, when such a system must respond to a rapidly varying control signal, a great deal of reactive power must necessarily be expended to drive the control grid.
The use of large amplitude control signals is particularly disadvantageous in gas discharge display systems where many control grids are used, such as in systems producing television images. In such cases, it becomes uneconomical to use anything but integrated circuit technology for building the control grid drivers. If large amplitude control signals (300-400 volts) are needed, the integrated circuit drivers become either impossible to manufacture or prohibitively expensive.
Another problem which exists when the above described type of cathodoluminescent system is used in a gas discharge display is that the resultant contrast ratio is somewhat small. Thus, even though large amplitude control signals must be used with the prior art systems, the degree to which even they can control the electron beam remains smaller than is desirable.